Image projection system and image projection method

ABSTRACT

An image projection system projects a plurality of same images on a plane of projection by superimposition. The image projection system includes a plurality of projectors configured to have mutually different resolutions and project the plurality of same images on the plane of projection, and an image data output device configured to output to the plurality of projectors image data corresponding to the plurality of same images with the resolutions of the plurality of projectors, respectively.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image projection system and an imageprojection method which are adapted to project two or more same imageson a plane of projection by superimposition.

2. Description of the Related Art

Conventionally, an image projection system which projects two or moresame images from two or more projectors on a plane of projection bysuperimposition (stack projection) is known. For example, see JapanesePatent No. 3908255.

In the image projection system disclosed in Japanese Patent No. 3908255,however, the combination of projectors usable for stack projection hasnot been flexible.

SUMMARY OF THE INVENTION

In an embodiment, the present invention provides an image projectionsystem which projects a plurality of same images on a plane ofprojection by superimposition, the image projection system including: aplurality of projectors configured to have mutually differentresolutions and project the plurality of same images on the plane ofprojection; and an image data output device configured to output to theplurality of projectors image data corresponding to the plurality ofsame images with the resolutions of the plurality of projectors,respectively.

Other objects, features and advantages of the present invention willbecome more apparent from the following detailed description when readin conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of an image projection system according to anembodiment.

FIG. 2 is a diagram showing a projection portion of a projector.

FIG. 3 is a diagram showing a state in which projection images in an ORarea between projection areas of first and second projectors on a screensurface are taken by a digital camera.

FIG. 4 is a block diagram showing a composition of a controller of theimage projection system according to the embodiment.

FIG. 5A is a diagram showing a content image on an external memory.

FIG. 5B is a diagram showing a dot pattern on a flash memory.

FIG. 6 is a flowchart for explaining a process performed by a controllerof the overall image projection system.

FIG. 7A is a diagram showing a state in which an image of a dot patternDP1 projected by a first projector is created by the digital camera.

FIG. 7B is a diagram showing a state in which an image of a dot patternDP2 projected by a second projector is created by the digital camera.

FIG. 8 is a flowchart for explaining a correction parameter receptionprocess.

FIG. 9A is a diagram showing a part of an image of a dot pattern DP1 ona first flash memory.

FIG. 9B is a diagram showing a part of an image of the dot pattern DP1created by the digital camera.

FIG. 10 is a diagram for explaining a target projection area aftercorrection.

FIGS. 11A, 11B and 11C are diagrams for explaining an example ofconversion of the coordinates of one of dots of the dot pattern DP1 intothe coordinates of the dot on a same-scale original image correspondingto the position of the dot on a mapped projection content image.

FIGS. 12A, 12B and 12C are diagrams for explaining an example ofconversion of the coordinates of one of dots of the dot pattern DP2 intothe coordinates of the dot on a low-resolution image, obtained from theoriginal image, corresponding to the position of the dot on a mappedprojection content image.

FIG. 13 is a flowchart for explaining a first correction imagegeneration process.

FIG. 14 is a flowchart for explaining a second correction imagegeneration process.

FIGS. 15A, 15B and 15C are diagrams for explaining resolutions ofprojection images when stack projection is performed using twoprojectors in comparative example 1, comparative example 2, and thepresent embodiment, respectively.

DETAILED DESCRIPTION OF EMBODIMENTS

A description will be given of embodiments with reference to theaccompanying drawings.

FIG. 1 is a side view of an image projection system 100 according to anembodiment. In the following, an XYZ three-dimensional rectangularcoordinate system in which the Y axis direction is set to be parallel toa vertical direction as shown in FIG. 1 is used.

As shown in FIG. 1, the image projection system 100 includes twoprojectors 10A and 10B (the projector 10B hidden by the projector 10A isnot illustrated), a digital camera 20, and a PC (personal computer) 30.In the following, the projector 10A will be referred to as a firstprojector 10A and the projector 10B will be referred to as a secondprojector 10B. The PC 30 is a controller of the image projection systemaccording to the embodiment.

For example, the first and second projectors 10A and 10B are arrayed ina line parallel to the X axis direction on a floor. In FIG. 1, thesecond projector 10B is disposed on the −X side of the first projector10A and hidden by the first projector 10A. Typically, the first andsecond projectors 10A and 10B are arranged on the −Y/−Z side of a hungtype screen S in proximity to each other at slanting downward portionsof the screen S. In this example, the screen S has a rectangularconfiguration, a longitudinal direction of the screen S is set to beparallel to the X axis direction, and an aspect ratio of the screen S isset to 4:3.

The first and second projectors 10A and 10B have mutually differentresolutions. In this example, the first projector 10A has a resolutionhigher than a resolution of the second projector 10B. Specifically, aresolution (real resolution) of the first projector 10A is 1280×800pixels, and a resolution (real resolution) of the second projector 10Bis 1024×768 pixels.

Each of the projectors 10A and 10B includes a housing 12 and aprojection portion 16 (see FIG. 2).

A transparent window member 22 that light penetrates is disposed in anupper wall of the housing 12 on the +Y side of the housing 12.

The projection portion 16 is accommodated in the housing 12 andconfigured to emit light which is modulated according to image data,onto the screen S via the transparent window member 22 so that an imageis projected on a surface of the screen S (screen surface).

FIG. 2 is a diagram showing the projection portion 16 of the projector10A or 10B. As shown in FIG. 2, the projection portion 16 includes alight source 80, a color wheel 82 as a light separation unit, a lightpipe 84 as a light equalization unit, two condenser lenses 86, 88 as alight refraction unit, two mirrors 90, 92 as a light reflection unit, adigital micromirror device (DMD) 94 as a light modulation unit, aprojection lens 96 as a light divergence and focusing unit, a mirror 97as a light reflection unit, and a free-surface mirror 98 as a lightdivergence and reflection unit.

The projection lens 96 has an optical axis direction parallel to the Yaxis direction and is implemented by two or more lens elements (notillustrated) which are arrayed at intervals of a predetermined distancealong the optical axis direction. An optical path of the light from thelight source 80 to the mirror 97 in the projection portion 16 isindicated by the arrows in FIG. 2.

In the projection portion 16, the light emitted from the light source 80is incident on the color wheel 82. The incident light is separated intothree color-component light beams by the color wheel 82 sequentially,and the color-component light beams are output by the color wheel 82 inthe time sequence. Each color-component light beam from the color wheel82 is incident on the light pipe 84. The luminance distribution of eachcolor-component light beam from the color wheel 82 is equalized by thelight pipe 84 and incident on the condenser lenses 86 and 88. After theposition of a focusing surface is adjusted, each color-component lightbeam incident on the condenser lenses 86 and 88 is reflected by themirrors 90 and 92 to enter the DMD 94. Each color-component light beamis modulated in accordance with the image information and reflected bythe DMD 94 to enter the projection lens 96. Each color-component lightbeam entering the projection lens 96 is diverged and reflected by themirror 97 to enter the free-surface mirror 98. Each color-componentlight beam entering the free-surface mirror 98 is diverged and reflectedby the free-surface mirror 98, and the color-component light beam fromthe free-surface mirror 98 is projected through the transparent windowmember 22 in a slanting upward direction toward the screen S on the+Y/+Z side of the housing 12 (see FIG. 1). As a result, a color image ora monochrome image is projected on the surface of the screen S.

The above-described projection portion 16 is configured as a short focussystem in which the focal position of the projection light is reduced.With a reduced projection distance, the projection portion 16 mayproject a color or monochrome image of an adequately large size on thescreen S. In other words, the projection portion 16 is configured as ashort focus system including an optical system in which a mirror havingrefractive power (the free-surface mirror 98) is provided. This mirrormay have positive or negative refractive power. Because the opticalsystem of the projection portion 16 includes the mirror having therefractive power, the size of an image projected on the screen S may beon the order of 80 inches even when a distance between the transparentwindow member 22 and the screen S is less than 50 cm.

The short-focus projector 10 as described above may project an image onthe screen S from a position near to the screen S, and undesiredintervention of a person or an object between the projector 10 and thescreen S may be prevented, so that the image projected on the screen Smay be prevented from being shaded by a person or an object interveningbetween the projector 10 and the screen S.

Further, in the image projection system 100 according to the embodiment,same images from the two projectors 10A and 10B with differentresolutions are projected on the screen surface by superimposition suchthat the projected images are exactly in agreement (stack projection),and a bright clear projection image (with high contrast and good colorreproduction property) may be obtained.

The digital camera 20 is positioned so that an OR area between aprojection area of the first projector 10A and a projection area of thesecond projector 10B on the screen surface may fit in an angle of viewof an imaging lens of the digital camera 20 (see FIG. 3). For example,the digital camera 20 is supported on a table via a tripod so that theOR area may fit in the angle of view of the imaging lens of the digitalcamera 20. The digital camera 20 individually creates an image of ahigh-resolution dot pattern DP1 and an image of a low-resolution dotpattern DP2 projected on the screen surface in a time sequence by thefirst and second projectors 10A and 10B, and outputs the resulting imagedata to the PC 30 respectively.

The PC 30 is disposed on the table and connected to the projectors 10A,10B and the digital camera 20 (for example, by USB connection).

FIG. 4 is a block diagram showing a composition of the PC 30 as thecontroller of the image projection system according to the embodiment.As shown in FIG. 4, the PC 30 includes a central processing unit (CPU)37, first through fourth frame memories 31 a-31 d, a correction datareceiver unit 32, a resolution converter unit 33, first and second imagedata correction units 34 a and 34 b, and first and second flash memories35 a and 35 b.

The CPU 37 controls respective component parts of the overall PC 30 andcontrols the digital camera 20.

The first frame memory 31 a temporarily stores image data supplied froman external memory 40 (a HDD, a USB memory, etc.) image by image, andsends the image data to the first image data correction unit 34 a viathe correction data receiver unit 32. The external memory 40 storesimage data of a content image (see FIG. 5A) to be projected.

The third frame memory 31 c temporarily stores image data supplied fromthe external memory 40 image by image, and sends the image data to theresolution converter unit 33 via the correction data receiver unit 32.

The correction data receiver unit 32 is configured to receive correctiondata (correction parameters) for correcting the image data from theexternal memory 40 based on image data of each of dot patterns DP1 andDP2 supplied from the digital camera 20.

In a case of a dot pattern projected on the screen surface, if thecorresponding projector does not face the screen S properly, trapezoidaldistortion may arise. In a case of a short focus projector, nonlineargeometric distortion may arise due to irregularities of the screensurface. To eliminate such distortion, the correction data receiver unit32 is configured to receive a distortion correction parameter forcorrecting such distortion. In a case of the stack projection, it isnecessary to correctly match the positions of images projected on thescreen surface by two or more projectors without deviation. To eliminatea deviation, the correction data receiver unit 32 is configured toreceive a deviation correction parameter for correcting a deviation ofthe images projected on the screen surface.

The resolution converter unit 33 is configured to convert a resolutionof the image data from the third frame memory 31 c into a resolution ofthe second projector 10B, and sends the resulting resolution to thesecond image data correction unit 34 b. The resolution conversion of theresolution converter unit 33 may be implemented by a bilinear or bicubicpixel interpolation technique.

The first image data correction unit 34 a is configured to correct theimage data from the first frame memory 31 a based on the correction dataof the dot pattern DP1 received by the correction data receiver unit 32,and sends the image data to the second frame memory 31 b. The firstimage data correction unit 34 a may include a distortion correction unitconfigured to correct distortion of the image data and a deviationcorrection unit configured to correct a deviation of the image data.

The second image data correction unit 34 b is configured to correct theimage data from the resolution converter unit 33 based on the correctiondata of the dot pattern DP2 received by the correction data receiverunit 32, and sends the image data to the fourth frame memory 31 d. Thesecond image data correction unit 34 b may include a distortioncorrection unit configured to correct distortion of the image data and adeviation correction unit configured to correct a deviation of the imagedata.

The second frame memory 31 b temporarily stores the image data suppliedfrom the first image data correction unit 34 a image by image, and sendsthe image data to the first projector 10A.

The fourth frame memory 31 d temporarily stores the image data suppliedfrom the second image data correction unit 34 b image by image, andsends the image data to the second projector 10B.

The first flash memory 35 a stores the image data of the high-resolutiondot pattern DP1. In this embodiment, the resolution of the dot patternDP1 is the same as the resolution of the first projector 10A. The CPU 37performs switching to select one of a first connection between thesecond frame memory 31 b and the first projector 10A and a secondconnection between the first flash memory 35 a and the first projector10A.

The second flash memory 35 b stores the image data of the low-resolutiondot pattern DP2. As described above, the resolution of the dot patternDP2 is lower than the resolution of the dot pattern DP1. In thisembodiment, the resolution of the dot pattern DP2 is the same as theresolution of the second projector 10B. The CPU 37 performs switching toselect one of a first connection between the fourth frame memory 31 dand the second projector 10B and a second connection between the secondflash memory 35 b and the second projector 10B.

For example, each of the dot patterns DP1 and D2 includes a set ofcircular black dots (black circles) arrayed in a 8×5 matrix form, asshown in FIG. 5B. The low-resolution dot pattern DP2 is created byscaling using the resolution conversion of the high-resolution dotpattern DP1. The dot pattern DP2 includes a set of circular black dotsarrayed in an 8×5 matrix form. In this way, if the number of dotsincluded in each of the dot patterns DP1 and DP2 is the same, the dotsize and the dot interval on the screen surface may be easily matchedbetween the dot pattern DP1 and the dot pattern DP2. The dot intervalcorresponds to the accuracy of geometric correction, and the accuracy ofgeometric correction may be easily matched between the dot patterns DP1and DP2 and the same dot size may be easily extracted in the dotextraction processing.

Next, a process performed by the image projection system according tothe embodiment is explained with reference to FIG. 6. FIG. 6 is aflowchart for explaining the process performed by the image projectionsystem according to the embodiment. The flowchart of FIG. 6 isequivalent to a processing algorithm of the CPU 37.

Initially, the first projector 10A is connected to the second framememory 31 b (the first connection) and the second projector 10B isconnected to the fourth frame memory 31 d (the first connection). A usermay instruct to the CPU 37 selection of a correction parameter settingmode using an input device (for example, a keyboard, a mouse, etc.)which is connected to the PC 30. Initially, the correction parametersare set to default values (initial settings).

As shown in FIG. 6, in step S1, the CPU 37 determines whether acorrection parameter setting request is received. When the selection ofthe correction parameter setting mode has not been requested by theuser, a result of the determination in step S1 is in the negative andthe control branches to step S10. When the selection of the correctionparameter setting mode has been requested by the user, a result of thedetermination in step S1 is in the affirmative and the control branchesto step S2.

In step S2, the CPU 37 switches the first connection between the framememories 31 b and 31 d and the projectors 10A and 10B to the secondconnection between the flash memories 35 a and 35 b and the projectors10A and 10B. Specifically, the CPU 37 performs switching to select thesecond connection between the first flash memory 35 a and the firstprojector 10A by disconnecting the second frame memory 31 b from thefirst projector 10A, and performs switching to select the secondconnection between the second flash memory 35 b and the second projector10B by disconnecting the fourth frame memory 31 d from the secondprojector 10B.

In step S3, the CPU outputs the image data of the dot pattern DP1 to thefirst projector 10A. Specifically, the image data of the dot pattern DP1are read from the first flash memory 35 a and sent to the firstprojector 10A by the CPU 37. As a result, an image of the dot patternDP1 is projected on the screen surface from the first projector 10A.

In step S4, an image of the dot pattern DP1 projected on the screensurface is created by the digital camera 20 (see FIG. 7A). The imagedata of the image created by the digital camera 20 are sent to thecorrection data receiver unit 32.

In step S5, the CPU 37 outputs the image data of the dot pattern DP2 tothe second projector 10B. Specifically, the image data of the dotpattern DP2 are read from the second flash memory 35 b and sent to thesecond projector 10B by the CPU 37. As a result, an image of the dotpattern DP2 is projected on the screen surface from the second projector10B.

In step S6, an image of the dot pattern DP2 projected on the screensurface is created by the digital camera 20 (see FIG. 7B). The imagedata of the image created by the digital camera 20 are sent to thecorrection data receiver unit 32.

In step S7, the CPU 37 causes the correction data receiver unit 32 toperform a correction parameter reception process. The correctionparameter reception process will be described later.

In step S8, the CPU 37 determines the correction parameters, which aresent to the first and second image data correction units 34 a and 34 b,by the received correction parameters, respectively.

In step S9, the CPU 37 switches the second connection between the flashmemories 35 a and 35 b and the projectors 10A and 10B to the firstconnection between the frame memories 31 b and 31 d and the projectors10A and 10B. Specifically, the CPU 37 performs switching to select thefirst connection between the second frame memory 31 b and the firstprojector 10A by disconnecting the first flash memory 35 a from thefirst projector 10A, and performs switching to select the firstconnection between the fourth frame memory 31 d and the second projector10B by disconnecting the second flash memory 35 b from the secondprojector 10B.

Subsequently, the CPU 37 reads from the external memory 40 the imagedata of the content image whose resolution is the same as the resolutionof the first projector 10A, and sends the image data to each of thefirst and third frame memories 31 a and 31 c. The image data sent to thefirst frame memory 31 a are supplied to the first image data correctionunit 34 a via the correction data receiver unit 32. The image data sentto the third frame memory 31 c are supplied to the second image datacorrection unit 34 b via the correction data receiver unit 32 and theresolution converter unit 33.

In step S10, the CPU 37 causes the first image data correction unit 34 ato perform a first correction image generation process. The firstcorrection image generation process will be described later.

In step S11, the CPU 37 causes the second image data correction unit 34b to perform a second correction image generation process. The secondcorrection image generation process will be described later.

Next, the correction parameter reception process (step S7) performed bythe correction data receiver unit 32 is explained with reference to FIG.8. FIG. 8 is a flowchart for explaining the correction parameterreception process.

As shown in FIG. 8, in step S7-1, the correction data receiver unit 32computes centroid coordinates of each of dots of the dot pattern DP1 inthe created image. In the following, for the sake of convenience, thecentroid of each of the dots of the dot pattern DP1 will also bereferred to as a lattice point.

The centroid coordinates of each dot of the dot pattern DP1 may becomputed in decimal pixel accuracy (in sub-pixel accuracy).Specifically, by using a known method, binarization of the image data isperformed, a group of black pixels is taken from the binary image databy pattern matching, and the centroid coordinates are computed indecimal pixel accuracy (see FIG. 9B). Similarly, the centroidcoordinates of each dot of the dot pattern DP1 on the first flash memory35 a are computed (see FIG. 9A).

In step S7-2, the correction data receiver unit 32 computes thecoordinates of the outer periphery of the projection area of the firstprojector 10A by extrapolation of the computed centroid coordinates ofthe respective dots.

Specifically, the coordinates of the outer periphery of the projectionarea of the first projector 10A are computed by a linear extrapolationof the computed centroid coordinates of the respective dots. Similarly,the coordinates of the outer periphery of the dot pattern DP1 on thefirst flash memory 35 a are computed.

For example, a corresponding point Q_(C) (see FIG. 9B) of the dotpattern DP1 in the image created by the digital camera 20 for a pointQ_(P) (see FIG. 9A) of the dot pattern DP1 on the first flash memory 35a may be determined based on a coordinate vector of respective centroidcoordinates of four adjoining dots A_(C), B_(C), C_(C), D_(C) of thepoint Q_(C) which are already computed, by the following formula (1):Q _(C)=(1−s)((1−t)A _(C) +tB _(C))+s((1−t)C _(C) +tD _(C))  (1)

It is assumed that the point Q_(P) is a point obtained by internaldivision of four adjoining lattice points A_(P), B_(P), C_(P), D_(P) ofthe point Q_(P) (the centroid coordinates of the dot are alreadycomputed) by t:(1−t) (0<t<1) in the x axis direction and internaldivision of the four adjoining lattice points by s:(1−s) (0<s<1) in they axis direction. In the example of FIG. 9B, it is assumed that −0.5<t<0and −0.5<s<0.

Although a nonlinear geometric distortion may arise in the overall dotpattern DP1, distortion which arises within a range (or its outerperipheral range) of a quadrilateral patch including 2×2 lattice pointsas a part of the dot pattern, whose area is sufficiently small, may beconsidered a linear geometric distortion.

In step S7-3, the correction data receiver unit 32 computes centroidcoordinates of each of dots of the dot pattern DP2 in the created image.In the following, for the sake of convenience, the centroid of each ofthe dots of the dot pattern DP2 will also be referred to as a latticepoint. The procedure of step S7-3 is essentially the same as that ofstep S7-1 described above.

In step S7-4, the correction data receiver unit 32 computes thecoordinates of the outer periphery of the projection area of the secondprojector 10B by extrapolation of the computed centroid coordinates ofthe respective dots. The procedure of step S7-4 is essentially the sameas that of step S7-2 described above.

Hence, the outer periphery coordinates of the projection areas of theprojectors on the dot patterns in the created images are computed basedon the coordinates of the lattice points of the dot patterns in thecreated images.

As a result, the projection areas (the surface areas where a white imageis fully projected) of the first and second projectors 10A and 10B aredetected (see FIG. 10).

In step S7-5, as shown in FIG. 10, the correction data receiver unit 32determines a post-correction target projection area (a maximum-sizecontent image area) where the content images after correction are to beprojected to an AND area between the projection areas of the first andsecond projectors 10A and 10B. Namely, in step S7-5, the maximum-sizecontent image area obtained by scaling with the aspect ratio of eachcontent image retained is mapped to the AND area of the two projectionareas.

Specifically, the maximum-size content image area is determined asfollows. The positions of the four corner points of each of theprojection areas of the dot patterns DP1 and DP2 (whose images arecreated by the digital camera 20) in the coordinate system of thedigital camera 20 are known and the positions of the four sides of therectangle of each of the projection areas (the upper side, the lowerside, the left-hand side, and the right-hand side thereof) are alsoknown. A rectangular region (indicated by the dotted line in FIG. 10)which is interposed between the upper side and the lower side of each ofthe projection areas of the projectors on the dot patterns in thecreated images and interposed between the left-hand side and theright-hand side of each of the projection areas is determined as the ANDarea between the projection areas of the first and second projectors 10Aand 10B. To this rectangular region, the maximum size content imageareas obtained by scaling with the aspect ratio of the content imagemaintained (in the example of the content image in FIG. 5A, the aspectratio: 4:3) are assigned. In the example of FIG. 10, there is a slightmargin in the vertical direction and centering is performed by insertingwhite space in each of the upper and lower sides of the content image.

In step S7-6, the correction data receiver unit 32 computes a distortioncorrection parameter for correcting distortion in the image data of theoriginal content image and a deviation correction parameter forcorrecting a deviation in the image data of the original content imageso that the content image may be projected on the post-correction targetprojection area.

Namely, in step S7-6, the centroid coordinates of each of the dots ofthe dot pattern DP1 in the created image are converted into thecoordinates of a same-scale content image corresponding to the positionson the mapped content image.

Specifically, a lattice point P₁ (4*Blk₁, 3*Blk₁) (where Blk₁ is alattice size of the dot pattern DP1) of the lattice points of the dotpattern DP1 on the first flash memory 35 a output to the first projector10A, as shown in FIG. 11A, is considered. The corresponding coordinates(Xcam1, Ycam1) of the lattice point P₁ on the projection image shown inFIG. 11B are computed, and the target projection area after correction,indicated by the rectangular dotted line in FIG. 11B, is mapped. In FIG.11C, the coordinates of the lattice point P₁ on the same-scale (highresolution) content image are determined.

Suppose that (X₀, Y₀) denotes the coordinates of the origin located atthe upper left corner of the mapped content image area on the createdimage in FIGS. 11B and R denotes a scaling factor of the content image.The pixel coordinates (Xcont1, Ycont1) of the content image to beprojected at the lattice point on the created image may be representedby the following formulas (2) and (3):Xcont1=(Xcam1−X ₀)/R  (2)Ycont1=(Ycam1−Y ₀)/R  (3)The distortion correction parameter is implemented by the pixelcoordinates (Xcont, Ycont) on the content image obtained for all thelattice points of the dot pattern DP1. This distortion correctionparameter is sent to the first image data correction unit 34 a.

In step S7-7, the centroid coordinates of each of the dots of the dotpattern DP2 in the created image are converted into the coordinates ofthe dot on the low-resolution image corresponding to the position of thedot on the mapped content image.

The conversion method used in step S7-7 is essentially the same as thatused in step S7-6 except that the dot pattern DP2 on the second flashmemory 35 b shown in FIG. 12A and the content image shown in FIG. 12Bcorrespond to the low-resolution image. The scaling factor R of thecontent image in this case is a scaling factor of the low-resolutionimage.

Next, the first correction image generation process (S10) is explainedwith reference to FIG. 13. FIG. 13 is a flowchart for explaining thefirst correction image generation process.

As shown in FIG. 13, in step S10-1, the first image data correction unit34 a determines the coordinates of the high resolution content image onthe second frame memory 31 b which are to be referenced for each of thedot positions of a first correction image.

In step S10-2, the first image data correction unit 34 a computes thecoordinates of the high resolution content image which are to bereferenced for each of other positions than the dot positions by linearinterpolation.

In step S10-3, the first image data correction unit 34 a generates thefirst correction image for the first projector 10A based on the highresolution content image for projection according to the coordinates(decimal fractions) to be referenced, by a bilinear or bicubic pixelinterpolation technique.

Next, the second correction image generation process (S11) is explainedwith reference to FIG. 14. FIG. 14 is a flowchart for explaining thesecond correction image generation process.

As shown in FIG. 14, in step S11-1, the second image data correctionunit 34 b determines the coordinates of the low resolution content imageon the fourth frame memory 31 d which are to be referenced for each ofthe dot positions of a second correction image.

In step S11-2, the second image data correction unit 34 b computes thecoordinates of the low resolution content image which are to bereferenced for each of other positions than the dot positions by linearinterpolation.

In step S11-3, the second image data correction unit 34 b generates thesecond correction image for the second projector 10B based on the lowresolution content image for projection according to the coordinates(decimal fractions) to be referenced, by a bilinear or bicubic pixelinterpolation technique.

As a result, a geometric distortion and a deviation in the image data ofthe high resolution content image (whose resolution is the same as theresolution of the first projector 10A), received from the externalmemory 40, are corrected (the image data in a state where the geometricdistortion and the deviation are eliminated), and the resulting imagedata are sent to the first projector 10A so that the corresponding imageis projected on the screen surface by the first projector 10A. Further,the high-resolution content image (whose resolution is the same as theresolution of the first projector 10A) received from the external memory40 is converted into a low-resolution content image, the geometricdistortion and the deviation in the image data are eliminated, and theresulting image data are sent to the second projector 10B so that thecorresponding image is projected on the screen surface by the secondprojector 10B. Accordingly, the two distortion-corrected projectionimages are displayed in the same size at the same position on the screensurface by superimposition.

The above-described image projection system 100 according to theembodiment projects two same images on the screen surface (a plane ofprojection) by superimposition, and includes the projectors 10A and 10Bconfigured to have mutually different resolutions and project the sameimages on the screen surface, and the PC 30 (an image data outputdevice) configured to output to the projectors 10A and 10B image datacorresponding to the images with the resolutions of the projectors 10Aand 10B, respectively.

In this case, the image data with the different resolutions of theprojectors are output to the projectors, so that the images with theresolutions of the projectors are projected on the screen surface by theprojectors and the two same images with the different resolutions aresuperimposed on the screen surface.

As a result, stack projection may be performed by combining theprojectors with different resolutions. Hence, in the image projectionsystem 100 according to the embodiment, the combination of projectorsusable for stack projection is not limited and the flexibility ofselecting the projectors may be increased.

On the other hand, in the image projection system according to therelated art, the combination of projectors usable for stack projectionhas not been flexible. Even when a user owns several projectors withdifferent resolutions, it has been necessary to purchase a new projectorwhose resolution is the same as a resolution of any of those projectorsin order to perform stack projection with the image projection systemaccording to the related art. Further, it has been necessary to selectthe projectors of the same resolution in order to perform stackprojection with the image projection system according to the relatedart. Hence, the combination of projectors usable for stack projectionhas not been flexible.

FIG. 15A and FIG. 15B are diagrams for explaining resolutions ofprojection images (indicated in a one-dimensional fashion) when stackprojection is performed using two projectors of the same resolution incomparative example 1 and comparative example 2, respectively. FIG. 15Cis a diagram for explaining resolutions of projection images (indicatedin a one-dimensional fashion) when stack projection is performed usingtwo projectors with different resolutions (the present embodiment). Thehorizontal axis indicates coordinates of horizontal pixels (pictureelements), and the vertical axis indicates a luminance value.

As shown in FIGS. 15A and 15B, in the comparative examples 1 and 2,stack projection is performed using two projectors of the sameresolution, the luminance value doubles when the projection images aresuperimposed. If the positioning of the images is accurate, theresolution of the superimposed images is the same as the resolution ofthe original images.

As shown in FIG. 15C, in the image projection system 100 according tothe embodiment, stack projection is performed using a high resolutionprojector 10A and a low resolution projector 10B. The resolution of thesuperimposed images obtained by using these projectors 10A and 10B islower than a resolution in a case where two high resolution projectorsare combined and higher than a resolution in a case where two lowresolution projectors are combined. The luminance value obtained byusing these projectors is also similar to the case of the resolution.

The resolutions of the image data are preset to the high resolution ofthe first projector 10A higher than the low resolution of the secondprojector 10B, and the PC 30 (the image data output device) includes theresolution converter unit 33 configured to convert the high resolutionof image data to be output to the second projector 10B into the lowresolution of the second projector 10B. In this case, the imagecorresponding to the high resolution image data may be projected withthe high resolution by using the first projector 10A with the highresolution and the second projector 10B with the low resolution.

In the image projection system 100 according to the embodiment, the PC30 (the image data output device) is configured to output to theprojectors 10A and 10B image data of the dot patterns DP1 and DP2 whoseresolutions are preset to the resolutions of the projectors 10A and 10B,respectively, in a time sequence. The image projection system 100includes the digital camera 20 (an imaging unit) configured to createimages of the dot patterns DP1 and DP2 which are projected on the screensurface by the projectors 10A and 10B in the time sequence. In thiscase, the correction data (correction parameters) of the image data maybe obtained based on the dot patterns in the images created by thedigital camera 20.

In the image projection system 100 according to the embodiment, the PC30 (the image data output device) includes an image data correction unitincluding a distortion correction unit configured to correct distortionof the image data to be output to the corresponding one of theprojectors based on the distortion correction data of the dot patternsin the created images. In this case, a distortion-corrected image inwhich the distortion is eliminated by the distortion correction unit maybe projected on the screen surface.

In the image projection system 100 according to the embodiment, the PC30 (the image data output device) includes an image data correction unitincluding a deviation correction unit configured to correct a deviationof the image data to be output to the projectors based on the deviationcorrection data of the dot patterns in the created images. In this case,a deviation-corrected image in which the deviation is eliminated by thedeviation correction unit may be projected on the plane of projectionaccurately.

In the above embodiment, same images from the two projectors withdifferent resolutions are projected on the display screen S bysuperimposition. The present disclosure is not limited to thisembodiment. Same images from three or more projectors with differentresolutions may be projected on the display screen S by superimposition.In either case, it is preferred that the image data from the externalmemory 40 are output to each of the projectors with the resolution ofthe corresponding one of the projectors.

In the above embodiment, the image data whose resolution is the same asthe high resolution of the first projector are read from the externalmemory 40 and sent to the first projector without changing theresolution, while the read image data are converted into low-resolutionimage data (whose resolution is the same as the low resolution of thesecond projector) and sent to the second projector. However, the presentdisclosure is not limited to this embodiment. For example, the imagedata whose resolution is the same as the low resolution of the secondprojector may be read from the external memory 40 and sent to the secondprojector without changing the resolution, while the read image data maybe converted into high-resolution image data (whose resolution is thesame as the high resolution of the first projector) and sent to thefirst projector. Further, image data with another resolution differentfrom the resolutions of the first and second projectors may be read fromthe external memory 40, converted into high-resolution image data (whoseresolution is the same as the high resolution of the first projector)and sent to the first projector, while the read image data may beconverted into low-resolution image data (whose resolution is the sameas the low resolution of the second projector) and sent to the secondprojector.

In the above embodiment, the surface of the hung type screen S isutilized as an example of the plane of projection. The presentdisclosure is not limited to this embodiment. For example, the plane ofprojection may be any of a surface of a screen fixed to a wall of abuilding, a surface of a wall of a building, a surface of cloth, asurface of a panel, a surface of a board, and a surface of a windshieldof a car.

In the above embodiment, the dots are arrayed in a matrix form. Thepresent disclosure is not limited to this embodiment. In short, the dotsin each of the dot patterns may be arrayed in a two dimensional form.

In the above embodiment, the dot pattern is used as the patternprojected on the screen S. The present disclosure is not limited to thisembodiment. For example, a grid pattern may be used instead as thepattern projected on the screen S. In this case, instead of the dots ofthe dot pattern, the intersections of straight lines of a grid patternmay be used or the rectangular areas surrounded by straight lines of agrid pattern may be used.

In the above embodiment, the dot pattern is implemented by an array ofblack circles (black dots) in a white background. The present disclosureis not limited to this embodiment. For example, the dot pattern may beimplemented by any of an array of white dots (white circles, whiteellipses, white polygons, etc.) in a black background, an array of blackpolygons in a white background, and an array of black ellipses in awhite ground. In the present disclosure, dots whose color is deeper thana background color of the dot pattern are referred to as black dots, anddots whose color is lighter than the background color of the dot patternare referred to as white dots. Namely, the black dots and the white dotsmay include halftone dots.

In the above embodiment, the image data of the dot patterns are storedin the flash memories connected to the projectors, respectively. Thepresent disclosure is not limited to this embodiment. For example, apattern generation unit may be connected to each of the projectors, andthe pattern generation unit may be configured to generate at least onepattern and send the generated pattern to each of the projectors.

The composition of the projection portion 16 is not limited to thecomposition in the above embodiment. The composition of the projectionportion 16 in the above embodiment may be modified suitably. Forexample, in the above embodiment, the light from the light source 80 ismodulated in accordance with image information by the DMD 94. However,the present disclosure is not limited to this embodiment. For example,the light source may be modulated and driven in accordance with imageinformation. In this case, instead of the DMD 94, any of atwo-dimensional MEMS scanner, a two-dimensional galvanometer scanner, aset of MEMS mirrors, a set of galvanometer mirrors, a transmission typeliquid crystal panel, and a reflection type liquid crystal panel may beused.

In the above embodiment, the PC 30 is utilized as the image data outputdevice. However, the present disclosure is not limited to thisembodiment. For example, another device configured to output image datato each of the projectors may be utilized. Specifically, any of a tabletterminal, such as a smart phone, a DVD player, a Blu-ray disc player,and a videoconference device configured to transmit and receive at leastimage data may be utilized as the image data output device.

In the above embodiment, the controller (the PC 30) is configured toread image data from the external memory 40 and output the image data tothe projectors 10A and 10B. However, the present disclosure is notlimited to this embodiment. For example, the controller may beconfigured to output to the projectors 10A and 10B image data read froman internal hard disk drive or image data distributed from the Internet.

In the above embodiment, the projection portion is configured into ashort focus system. However, the projection portion may not be a shortfocus system. In such a case, a MEMS (microelectromechanical system)mirror or a galvanometer mirror may be used instead of the mirror havinga refractive power (the free-surface mirror 98).

As described in the foregoing, with the image projection systemaccording to the present invention, the flexibility in selecting theprojectors usable for stack projection may be increased.

The image projection system according to the present invention is notlimited to the above-described embodiments, and variations andmodifications may be made without departing from the scope of thepresent invention.

The present application is based upon and claims the benefit of priorityof Japanese Patent Application No. 2013-051153, filed on Mar. 14, 2013,the content of which are incorporated herein by reference in theirentirety.

What is claimed is:
 1. An image projection system which projects aplurality of same images on a plane of projection by superimposition,comprising: a plurality of projectors configured to have mutuallydifferent resolutions and project the plurality of same images on theplane of projection; and a processor to output to the plurality ofprojectors image data corresponding to the plurality of same images withthe resolutions of the plurality of projectors, respectively, whereinthe resolutions of the image data are preset to a highest resolution ofa first projector among the resolutions of the plurality of projectors,and the processor includes a resolution converter configured to convertthe highest resolution of image data to be output to one of theplurality of projectors other than the first projector into a resolutionof said one of the plurality of projectors.
 2. The image projectionsystem according to claim 1, wherein the processor is configured tooutput to the plurality of projectors image data of a plurality ofpatterns whose resolutions are preset to the resolutions of theplurality of projectors, respectively, in a time sequence, and the imageprojection system further comprises an imaging device configured tocreate images of the plurality of patterns projected on the plane ofprojection in a time sequence by the plurality of projectors.
 3. Theimage projection system according to claim 2, wherein the processorincludes an image data correction unit configured to correct the imagedata to be output to the plurality of projectors based on the pluralityof patterns in the created images.
 4. The image projection systemaccording to claim 3, wherein the image data correction unit includes adistortion correction unit configured to correct distortion of the imagedata to be output to the plurality of projectors based on distortioncorrection data of the plurality of patterns in the created images. 5.The image projection system according to claim 3, wherein the image datacorrection unit includes a deviation correction unit configured tocorrect a deviation of the image data to be output to the plurality ofprojectors based on deviation correction data of the plurality ofpatterns in the created images.
 6. The image projection system accordingto claim 2, wherein the plurality of patterns include a plurality of dotpatterns in which dots are arrayed in a two dimensional form.
 7. Animage projection method which projects a plurality of same images on aplane of projection by superimposition, comprising: outputting to aplurality of projectors having mutually different resolutions image datacorresponding to the plurality of same images with the resolutions ofthe plurality of projectors, respectively; and projecting the image databy the plurality of projectors, wherein the resolutions of the imagedata are preset to a highest resolution of a first projector among theresolutions of the plurality of projectors, and the outputting the imagedata includes converting, by a resolution converter unit, the highestresolution of image data to be output to one of the plurality ofprojectors other than the first projector into a resolution of said oneof the plurality of projectors.
 8. The image projection method accordingto claim 7, wherein the outputting the image data includes: outputtingto the plurality of projectors image data of a plurality of patternswhose resolutions are preset to the resolutions of the plurality ofprojectors, respectively, in a time sequence; creating images of theplurality of patterns projected on the plane of projection in a timesequence by the plurality of projectors; and correcting the image datato be output to the plurality of projectors based on the plurality ofpatterns in the created images.